1. Field of the Invention
The present invention relates to a projective capacitive touch apparatus and a method for identifying touched positions. More particularly, the present invention relates a projective capacitive touch apparatus for identifying distinctive touched positions and a method for identifying distinctive touched positions.
2. Descriptions of the Related Art
In the past, interaction with computers or machines was mainly through keyboards and mice as interfaces. With the advancement of science and technology, product designs are evolving towards more user-friendly human-machine interfaces (HMIs), among which touch panels have become very popular input devices and have found a wide application in personal computers, notebook computers, personal digital assistants (PDAs), mobile phones, automatic teller machines (ATMs), various ticket machines and the like. This kind of intuitive input devices allows the user to activate desired functions directly on a screen without need of keyboards, mice or other additional input devices. This helps to reduce the volume and weight of the final product and presents a more pleasing appearance.
The popular touch schemes currently available fall into the following five categories: the resistive touch scheme, the capacitive touch scheme, the surface acoustic wave touch scheme, the optical touch scheme and the electromagnetic touch scheme, each of which has respective advantages and disadvantages and is applicable to different fields.
As the touch technology advances, the concept of multi-touch has been proposed and developed. As compared to the conventional single-touch input mode, the multi-touch input mode allows the user to perform more complex and diversified functional operations. Among the various touch schemes, the resistive and the surface acoustic wave touch schemes fail to accomplish the multi-touch function as restricted by the induction principle thereof. The electromagnetic induction touch scheme necessitates the use of a dedicated electromagnetic pen, which is unfavorable for the multi-touch application. The optical touch scheme, although allowing detection of distinctive positions in the multi-touch mode, requires an installation of a corresponding reflecting light receiver, which makes the touch system relatively bulky and inapplicable to low-profile or miniaturized screens.
Consequently, the capacitive induction touch scheme becomes the preferred option that allows for the multi-touch function. As compared to other touch schemes, the capacitive induction touch panel only needs to be touched slightly by a finger without pressing. Furthermore, the capacitive induction touch screens feature high resolution, high light transmittance and multi-touch function, and are suitable for use in low-profile and miniaturized screens.
According to the capacitive induction touch scheme, the coordinates of the touched position is detected by sensing a current generated at the touched position in response to the capacitance variation arising from the static induction between the transparent electrode and finger. The capacitive induction touch scheme is divided into two categories according to the different induction principles: the surface capacitive touch scheme and the projective capacitive touch scheme. However, the surface capacitive touch scheme is only able to detect a single-touch, so only the projective capacitive touch scheme allows for multi-touch detection.
FIG. 1 is a schematic view illustrating the structure of a conventional projective capacitive touch apparatus 1. The projective capacitive touch apparatus 1 comprises a protective layer 11, a display device 12, a projective capacitive touch panel 13 and a controller 14. The protective layer 11, which is the uppermost layer of the projective capacitive touch apparatus 1, is made of a transparent material. The display device 12, which is the lowermost layer of the projective capacitive touch apparatus 1, is configured to project an image upwards. The projective capacitive touch panel 13 is disposed between the protective layer 11 and the display device 12 and is electrically connected to the controller 14.
In reference to FIG. 2, the projective capacitive touch panel 13 is formed with two sets of sensing electrodes-non-parallel to each other. The two sets of sensing electrodes are crossed with each other and correspond to different coordinate axes respectively. Each set of sensing electrodes has a plurality of sensing electrodes. For example, the projective capacitive touch panel 13 has a plurality of X-axis sensing electrodes 131 and a plurality of Y-axis sensing electrodes 132, in which an X-axis sensing electrode 131x intersects a Y-axis sensing axis 132y at the touched position 133.
Due to biological electrostatic charges, a variation in the induced capacitance and potential difference will occur at the touched position 133 on the projective capacitive touch panel 13 corresponding to the position being touched. This results in a potential variation and a very small induced current in the X-axis sensing electrode 131x and the y-axis electrode 132y crossing the touched position 133. Hence, by detecting such potential variation and/or an induced current, the projective capacitive touch panel 13 generates a set of reference signals and transmits it to the controller 14, which then generates a set of coordinate values according to the set of reference signals. According to this set of coordinate values, an application determines which function the user wants to execute.
FIG. 3 is a schematic view illustrating a case when the user touches two points on the projective capacitive touch apparatus 1 simultaneously. When the user touches two distinct positions on the protective layer 11 simultaneously, an induced capacitance will be generated at the first touched position 133a and the second touched position 133b of the projective capacitive touch panel 13 respectively. Then, a potential variation and induced current will occur in the first X-axis sensing electrode 131a and the first Y-axis sensing electrode 132a crossing the first touch position 133a respectively, as is also the case when the second X-axis sensing electrode 131b and second Y-axis sensing electrode 132b crosses the second touch position 133b. 
However, in this case, the potential variations and/or induced currents corresponding to the two X-axis coordinate axes and the two Y-axis coordinate axes respectively will be detected by the projective capacitive touch panel 13 simultaneously and in turn be identified as two X-coordinate values and two Y-coordinate values. These X-coordinate values and Y-coordinate values can be combined arbitrarily to represent four touched positions, namely, the first touched position 133a, the second touched position 133b, the third touched position 133c and the fourth touched position 133d. Among the four touched positions, the third touched position 133c and the fourth touched position 133d are known as ghost touched positions, i.e., they are not actual positions where the user touches. Accordingly, the controller 14 is unable to identify which of the four touched positions are the actual positions where the user touches according to these X coordinate values and Y coordinate values, i.e., the controller 14 is incapable of identifying the first touched position 133a and the second touched position 133b, which renders it impossible for the projective capacitive touch sensing device 1 to provide a multi-touch function.
In view of this, it is highly desirable in the art to provide a projective capacitive touch sensing apparatus capable of identifying distinctive touched positions and a method for identifying distinctive touched positions.